getopts

Basic option parsing in a script

$ while getopts "ab:c" opt; do case $opt in a) echo "Option a";; b) echo "Option b with arg: $OPTARG";; c) echo "Option c";; esac; done

$ getopts "f:o:v" opt

$ getopts ":ab:c" opt

$ shift $((OPTIND - 1))

$ case $opt in \?) echo "Invalid option: -$OPTARG";; esac

getopts OPTSTRING NAME [ARGS]

getopts is a POSIX shell builtin for parsing short command-line options in scripts. It processes options one at a time, typically used in a while loop with a case statement to handle each option.
Options are single characters preceded by a dash (e.g., -a, -b). Options can be combined (-abc). Options requiring arguments can have the argument immediately following (-ffile) or as the next argument (-f file).
When all options are processed, getopts returns a non-zero exit status. After parsing, use shift $((OPTIND - 1)) to remove processed options, leaving remaining arguments in $@.

OPTSTRING

String of option characters. A colon after a character indicates it requires an argument. A leading colon enables silent error mode.

Variable name to store the current option character.

Optional arguments to parse instead of positional parameters.

OPTIND

Index of the next argument to be processed. Initialized to 1.

Contains the argument for options that require one, or the invalid option character in silent mode.

Set to 0 to suppress error messages.

getopts only handles short options (single character). For long options (--verbose), use the external getopt command instead. The OPTIND variable must be reset to 1 if parsing multiple argument sets. Option processing stops at the first non-option argument or at --.

getopts is defined by the POSIX standard and available in all POSIX-compliant shells including bash, dash, ksh, and zsh. It was introduced as a more portable alternative to the external getopt utility, which varies between systems. The builtin ensures consistent behavior across different Unix-like platforms.

getopt(1), bash(1), shift(1)